1. Field of the Invention
The present invention relates to an improved process for the conversion of an aromatic hydrocarbon in the presence of a titanium subfluoride on an inorganic oxide catalyst.
The invention is described with reference to alkylation, e.g., the synthesis of ethylbenzene or cumene by alkylation of benzene with ethylene or propylene in the presence of the catalyst. The invention can also be used in alkylaromatic transalkylation and isomerization.
2. Description of the Prior Art
Conversion of aromatic hydrocarbons is well known in industry. Some of the aromatic conversion reactions which occur include alkylation of aromatic hyrocarbons with an alkylating agent such as an olefin, disproportionation or transalkylation of alkyl aromatics and isomerization of alkyl aromatics such as xylenes, and of dialkyl and higher substituted aromatics.
Of special interest, has been the alkylation of benzene to ethylbenzene, or cumene. Ethylbenzene may be dehydrogenated to make styrene, while cumene is used for the production of phenol and acetone. Cumene is also dehydrogenated to form methylstyrene, in a process similar to that used to convert ethylbenzene to styrene. Ethylbenzene and cumene may also be used as blending components in aviation gasoline because of their high octane number.
It is well known that cumene can be synthesized from benzene and propylene using a catalyst of AlCl.sub.3, SPA or BF.sub.3. SPA is a generally accepted abreviation for solid phosphoric acid catalyst, or phosphoric acid which is adsorbed on kieselguhr or other support.
Ethylbenzene can be synthesized from benzene and ethylene using AlCL.sub.3 but SPA is not used commercially for this purpose. AlCl.sub.3 is a very popular alkylation catalyst, because of its high activity. Unfortunately, the catalyst operates as a slurry or sludge which is messy to handle on a commercial scale, and also is corrosive. The highly reactive nature of this Friedel-Crafts metal halide catalyst, AlCl.sub.3, is desirable when attempting to alkylate benzene with ethylene, because less active catalyst systems do not work.
Another highly selective catalyst system has been developed for the alkylation of benzene with olefins. This catalyst comprises boron trifluoride. The boron trifluoride catalyst system is exceptionally active and permits operation with dilute olefin streams, but it requires the continuous addition of BF.sub.3 to maintain catalyst activity. High catalyst activity also leads to oligomerization of olefins so that the contact time of olefins with BF.sub.3 catalyst should be as short as possible. This catalyst is also exceptionally water sensitive, as water not only destroys the catalyst, but produces very corrosive solutions which attack downstream processing units. BF.sub.3 also frequently appears in the product, and must be removed therefrom.
Because of the interest in alkylating benzene with olefins, and because of the inadequacies of existing catalyst systems, we studied the work that others and done, and made exhaustive investigations to determine if it would be possible to find a catalyst which would have the activity and selectivity required to produce an acceptable product, while making maximum use of existing petroleum resources.
A highly active catalyst was sought, to permit operation at lower temperatures with less utility cost, cost of construction, and to operate with less catalyst. In new units this would mean smaller, and cheaper reactor vessels, while in existing units it would mean that an increase in capacity could be obtained by changing catalyst in an existing reactor vessel with minor modification.
High selectivity is necessary, not only to permit operation with feedstreams which are not 100% pure olefin, but also to maximize production of the desired product, and to minimize production of polymerized olefins, or polyalkylated aromatic compounds.
Accordingly, many catalyst systems were studied to find a catalyst with excellent activity and selectivity, which was not corrosive or destroyed by water.
There has been extensive work done with Ti catalysts, though most work occurred in conjunction with studies of Ziegler-Natta catalysts. The closest prior art known in U.S. Pat. No. 2,381,481 (Class 260-683.15), U.S. Pat. No. 2,951,885 (Class 260-671), U.S. Pat. No. 2,965,686 (Class 260-671) and U.S. Pat. No. 3,153,634 (Class 252-429).
In U.S. Pat. No. 2,381,481, preparation and use of a catalyst prepared by treating alumina gel with fluotitanic acid is disclosed. This catalyst is used for polymerization of olefins to heavier hydrocarbons, and also for alkylation of parafins with olefins, the latter when operating at high temperatures, between 700.degree. and 900.degree. F. or higher. No mention is made of alkylation of aromatics with olefinic hydrocarbons or transalkylation of polyalkylbenzenes.
In U.S. Pat. No. 2,951,885, there is disclosed the use of titanium trihalide on activated alumina or other activated acidic oxide for alkylation of benzene with olefins. The catalyst is originally a tetrachloride, subsequently reduced to the trichloride with an alkali metal such as sodium, lithium, or potassium. The examples show that this catalyst will alkylate benzene with ethylene.
In U.S. Pat. No. 2,965,686, the thrust of the application was to develop a titanium subchloride catalyst. The subchloride catalyst was prepared by reacting titanium metal, in the form of turnings, with titanium tetrachloride. The patentee speculated, but gave no examples, showing that it would be possible to form the subchloride by reduction of titanium tetrachloride with hydrogen. The patentee did not believe the difficulties to be encountered would justify reduction of hydrogen.
In U.S. Pat. No. 3,153,634, there is disclosed the use of titanium subhalides in a polymerization reaction. The patentee is probably describing catalyst to make solid polymer, as he discusses production of solid polymer products. The patentee seems to teach that the halides all act equivalently. The patentee in U.S. Pat. No. 3,153,634 taught the very antithesis of applicants process, on page 3 lines 65-75 where he mentions use of benzene as an inert solvent to hold dissolved olefins, rather than as a reactant.
Accordingly, work continued on developing an improved process for the catalytic conversion of aromatic hydrocarbons.